Regression analysis of biologically effective integrated irradiances versus ozone,clouds and geometric factors |
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| Institution: | 1. Department of Environmental Sciences and Engineering, Xi''an Jiaotong University, Xi''an, China;2. Key Lab of Aerosol, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi''an, China;3. Air Quality Research Division, Environment Canada, Toronto, Canada;4. School of Architecture, Xi''an University of Architecture and Technology, Xi''an 710055, China |
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| Abstract: | Factors affecting UV radiation at the earth’s surface include the solar zenith angle, earth–sun distance, clouds, aerosols, altitude, ozone and the ground’s albedo. The variation of some factors, such as solar zenith angle and earth–sun distance, is well established. Total column ozone and UV radiation are inversely related, but the presence of clouds may affect the resulting UV in such a way that a depletion in the total column ozone may not always lead to an increase in the radiation at the earth’s surface. The aim of this paper is to determine the contribution to the variation of the biologically effective irradiance by geometric factors, clouds and ozone, jointly and separately, in Ushuaia (54°49′S, 68°19′W, sea level), and the seasonal variation of this relationship, given the magnitude and seasonal distribution of the ozone depletion and the frequent presence of high cloud cover in this site. For this purpose, multivariate and simple regression analyses of daily and monthly integrated irradiances weighted by the DNA damage action spectrum as a function of total column ozone and the integrated irradiances in the band 337–342 nm (as a proxy for cloud cover and geometric factors) have been performed. For the analysed period (September 1989–December 1996) more than 97% of the variation of the DNA damage weighted daily integrated irradiances is described by changes in ozone, clouds and geometric factors. Simple regression analysis for daily integrated irradiances, grouped by month, shows that most of this variation is explained by clouds and geometric factors, except in spring, when strong ozone depletion occurs intermittently over this area. When monthly trends are removed, similar results are observed, except for late winter. |
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